This invention relates to an ultraviolet radiation starting source, or ultraviolet (UV) enhancer, for a metal vapor arc discharge lamp.
High pressure metal halide arc discharge lamps typically comprise an arc tube which encloses an ionizable fill material and two electrodes at opposing ends of the tube. To reduce the time it takes to start the lamp, a starter electrode may be disposed inside the arc tube near one of the main electrodes, as shown in Freese et. al., U.S. Pat. No. 3,900,761. A discharge can be initiated between the starter electrode and one of the main electrodes at a voltage that is much lower than the voltage required to ignite an arc between the two main electrodes. The ultraviolet radiation and plasma from this discharge enhance discharge formation in the arc tube between the two main electrodes.
Zaslavsky et. al., U.S. Pat. No. 4,818,915, issued Apr. 4, 1989, discloses a UV enhancer which is separate from the arc tube. The '915 patent, which is incorporated herein by reference, describes a UV enhancer which typically has a borosilicate glass envelope enclosing an ionizable fill material and a single electrode. The single electrode has a getter which removes certain gases when the envelope heats and outgasses. These gases, particularly oxygen, hydrogen, and nitrogen, contaminate the fill material. When energized, the UV enhancer produces ultraviolet radiation which illuminates the path between the main electrodes within the arc tube, thus decreasing the time for generating a high intensity arc discharge.
The use of a getter increases the number of components in the UV enhancer, limits how small the UV enhancer can be made, and limits the operation of the UV enhancer to a particular temperature range. With a getter, the UV enhancer is sensitive to location within the lamp because of outgassing and the getter temperature range. Because of these size and location requirements, a UV enhancer with a getter cannot be used for all applications, such as double-ended lamps which have a small diameter outer envelope.
A typical process for making a UV enhancer begins with fabricating an electrode assembly which is inserted into a tube. The electrode assembly typically has a number of welded parts. As described in the '915 patent, an electrode assembly may include a moly foil which is welded to a rod and to an outer lead. The rod supports a getter, and the outer lead is coupled to a main electrode. Since the parts are welded, it can be difficult to produce UV enhancers with an automated system. Electrode assemblies are fabricated first, then manually loaded onto trays.
It is an object of the present invention to provide an improved UV enhancer.
It is another object of the present invention to provide a simplified method for manufacturing a UV enhancer.
It is yet another object of the present invention To provide a UV enhancer with fewer components then prior art devices.
It is still another object of the present invention to provide a UV enhancer which operates under a broad range of conditions.